Thin Film Transistor is an electronic device commonly used in the technical field of manufacture of liquid crystal display. Similar to Field Effect Transistor, a normal turn-on condition of the thin film transistor is a voltage difference between a gate and a source being larger than a threshold voltage, that is, the thin film transistor is turned on only when the voltage difference between the gate and the source is larger than the threshold voltage, otherwise the thin film transistor cannot be turned on.
With the increase of operation time of a thin film transistor, the threshold voltage of the thin film transistor will change, that is, a threshold voltage drift phenomenon will occur. For example, in a common case, the threshold voltage of the thin film transistor is 15V, that is, when the voltage difference between the gate and the source is lower than 15V, the thin film transistor cannot be turned on to operate. However, when a threshold voltage drift of 1V occurs, the thin film transistor can be turned on to operate normally only when the voltage difference between the gate and the source is not lower than 16V. It can be seen that the threshold voltage drift phenomenon of the thin film transistor has an effect on the normal turn-on of the thin film transistor and in turn on the operation of the thin film transistor such that the thin film transistor cannot operate normally in a circuit structure to achieve its function.
Thin Film Transistor Liquid Crystal Display (TFT-LCD) is a common liquid crystal display product. In the TFT-LCD, each pixel has a thin film transistor which is connected to a corresponding gate driving circuit so as to control variation of light transmission rate of the liquid crystal molecules in the pixel, such that a purpose of controlling the color variation of the pixel can be achieved. The GOA circuit technology is a gate driving circuit technology commonly used in the present TFT-LCD art, in the GOA circuit technology, the gate driving circuit is directly prepared on the array substrate, and thus the GOA circuit occupies a small space, has a simple preparation process, and has a good prospect in application.
The GOA circuit is a circuit corresponding to a row of pixels in the TFT-LCD and used for supplying a gate driving voltage for the thin film transistors in the corresponding row of pixels. The whole TFT-LCD has a plurality of rows of pixels and thus has a plurality of corresponding GOA circuit. FIG. 1 shows a schematic diagram of a liquid crystal panel including GOA circuits, wherein the GOA circuits are located at edges of the panel. During the operation of the TFT-LCD, each of rows of pixels is supplied with a gate driving voltage sequentially, and accordingly each of the GOA circuits corresponding to each of the rows of pixels starts to operate sequentially. FIG. 2 shows a schematic structural diagram of a GOA circuit corresponding to a certain row of pixels as shown in FIG. 1 (FIG. 2 is also a schematic structural diagram of the GOA circuit commonly used at present). It can be seen from FIG. 2 that the GOA circuit includes a plurality of thin film transistors and a capacitor, and the operation of the GOA circuit includes: a receiving terminal receives an input signal INPUT, and an output terminal outputs an output signal OUTPUT under the control of the individual thin film transistors, the capacitor and a clock signal.
With development of thin-film transistors industry and improvement of manufacturing process, the GOA technology has been applied to an increasing number of products, its advantages of reduced cost and simplified process have been respected by various major manufacturers, and the GOA technology has a high competitiveness in the market. However, there are some disadvantageous in the GOA technology: with increase in operation time, a phenomenon of threshold voltage drift will appear in the thin film transistors constituting the GOA circuit, which will cause deterioration of the stability of the thin film transistors and in turn affects the performance of the whole GOA circuit, especially when the thin film transistor for controlling a signal output terminal in the GOA circuit has a threshold voltage drift, the normal output of the GOA circuit will be seriously affected and the normal operation of the LCD display will be ultimately affected.
In the GOA circuit as shown in FIG. 2, the thin film transistor for controlling an output signal of the GOA circuit is an thin film transistor at the output terminal (as shown in the circle part in FIG. 2), which has a drain for receiving an output clock signal CLK. The threshold voltage drift data shown in FIG. 3 can be obtained by monitoring the thin film transistor at the output terminal under the room temperature (the temperature is 27° C.). It can be seen from FIG. 3 that the threshold voltage drift ΔVth (vertical axis) of the thin film transistor at the output terminal increases with the increase of the operation time (horizontal axis), which means that, with the increase of the operation time, if the turn-on voltage supplied to the thin film transistor at the output terminal is the normal turn-on voltage and keeps unchanged always, the thin film transistor at the output terminal will not be turned on after its threshold voltage drifts, and the whole GOA circuit in turn cannot output the output signal normally.
In summary, the threshold voltage drift phenomenon of the thin film transistor will seriously affect the normal turning-on of the thin film transistor, thereby affecting the normal operation of the circuit configuration including the thin film transistor; in the GOA circuit, the normal output of the whole GOA circuit will be directly affected if the thin film transistor for controlling the signal output has a threshold voltage drift.